We will screen up to 58 healthy volunteers with the goal of enrolling up to 48 subjects to participate in the study. Two cohorts will be studied. One cohort of healthy subjects will be studied with bronchoscopy and BAL (up to n = 12) at a single time point. This will provide lung and blood cells to assess immunophenotypes of resident pulmonary cells in the absence of any inflammatory stimulus. The cells will be studied with flow cytometry and with cell culture. Cell-associated and secreted miRNA will be studied ex vivo over a 6-24 hour period. A second cohort of subjects (n = 36) will be studied after undergoing segmental endotoxin challenge with bronchoscopy. BAL will be performed at either 6 (n=12), 24 (n=12) or 48 hours (n=12) after this challenge. Subjects who participated in the first cohort will be eligible to participate in the 2nd cohort with endotoxin challenge after a 4-week interval from their earlier participation. The cells acquired with BAL at these 3 time points will provide a means to study changes in secreted and cell associated miRNA and their relation to specific cell types. The protocol was approved on 01/26/2015. We enrolled our first subject on 06/18/2015 and to date we have enrolled 25 subjects Seven subjects completed the control arm of the study (without endotoxin, single bronchoscopy) Two of the subjects have participated in both the control (non-endotoxin) and the endotoxin challenge portions of the study Fourteen subjects with endotoxin challenge were completed. Four subjects signed a screening consent but did not qualify One subject signed a screening and bronchoscopy consent but withdrew before undergoing the bronchoscopy One subject signed a screening consent but was a no show on the study day.